In Transmission Mode 8 (TM8) of the LTE-Advanced standard, an evolved Node B (eNodeB or eNB) conventionally determines the Channel Quality Indicator (CQI) for the Physical Downlink Shared Channel (PDSCH) as Single Antenna Port, port 0, if the User Equipment (UE) is configured without Precoding Matrix Indicator/Rank Indicator (PMI/RI) reporting and if the number of Physical Broadcast Channel (PBCH) antenna ports is one. Otherwise, a diversity transmission technique is used. That is, for TM8, an eNodeB determines CQI for PDSCH based a non-beamformed CQI from the UpLink (UL) control channel signaling feedback from a UE. The eNodeB estimates CSI from the UpLink (UL) Sounding Reference Signals (SRS) sent from the UE, and the difference between the non-beamformed CQI and the beamformed CQI is compensated by eNodeB.
This conventional approach for TM8 is logical particularly if the UE is only able to see the downlink channel with a reduced column vector from the downlink link adaptation reference signal or if the total number of downlink transmission antennas is less than or equal to 2, in which case the gain from beamforming is nonexistent or is insignificant.
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